1. Field of the Invention
The present invention relates to a hydraulic driving device for an operating machine, and in particular, to a hydraulic driving device for an operating machine provided with a hydraulic control valve that controls an oil pressure in accordance with an operation of an operator.
2. Description of the Related Art
An operating machine, for instance, a battery forklift is provided with an electric pump as a hydraulic power source to move a fork included therein vertically. A hydraulic fluid supplied from the electric pump is supplied to a hydraulic control valve (for instance, a proportional solenoid valve). A supply state of the hydraulic fluid supplied to the hydraulic control valve is controlled by an unloading valve. The hydraulic control valve adjusts an oil pressure of the supplied hydraulic fluid to an oil pressure in accordance with an operation of an operator, for instance, an operation of a joystick and supplies the adjusted oil pressure to an actuator that moves the fork.
In such a battery forklift, when the joystick is not operated, a power source of a motor to drive the electric pump is turned off so that consumption of power accumulated in a battery is suppressed. This time, each of the unloading valve and the hydraulic control valve is controlled, thereby producing a state of closing an oil passage through which the hydraulic fluid between the electric pump and the actuator flows.
When an operation command in accordance with the operation of the joystick is inputted in the state as described above, starting the motor of the electric pump and opening the unloading valve and the hydraulic control valve are performed simultaneously. Consequently, a timing in which the oil pressure of the hydraulic fluid from the electric pump is exerted on the hydraulic control valve and a timing in which the hydraulic control valve moves a spool thereof to adjust the oil pressure of the supplied hydraulic fluid to a predetermined oil pressure occur simultaneously. For this reason, the oil pressure of the hydraulic fluid discharged from the electric pump is directly exerted on the actuator of the fork to generate a shock.
Japanese Patent Laid-Open Publication No. 2000-81905 discloses that, so as to suppress the shock, the hydraulic control valve is controlled in such a manner that an oil pressure is gradually increased. In this case, however, a change of the oil pressure in response to the operation of the joystick is slower and responsiveness thereof is deteriorated.
The present invention, in view of the foregoing problems, has an object of providing a hydraulic control device for an operating machine that suppresses a shock caused by hydraulic variations at the time of starting the pump.